This invention relates to shipping containers, and, more particularly, to an improved container for shipping refrigerated materials.
Vast quantities of frozen foods, produce, medical supplies, and other materials are shipped in refrigerated transportation containers every year. Traditionally, these containers are constructed of steel support structures with steel floors, walls, and roofs. Steel is generally used so as to provide sufficient strength, support, and rigidity to bear the heavy loads the containers carry and to withstand the rigors of loading and unloading. These containers have several drawbacks. First, because of the weight of the steel and the size of the containers, the weight of the container can easily approach 14,000 pounds. Additionally, steel, like many metals, is a relatively good thermal conductor. Accordingly, containers constructed of all steel components do not insulate very well. This is because the cold air inside the container has an easy path out of the container along the steel components.
In addition to being made of heavy material such as steel, traditional refrigeration containers have utilized traditional refrigeration systems, including compressors and coils, to keep the materials inside the container cold. Such systems have several drawbacks. One of these is that the compressor and other components in the system may break down and need costly or time consuming repairs. Additionally, the systems are run on electricity, and therefore require a source of electricity during transportation.
Accordingly, various non-mechanical refrigeration systems have been attempted. One such system is disclosed in U.S. Pat. No. 4,761,969 to James S. Moe, the present Applicant. This system utilizes a false ceiling inside a shipping container as the cooling chamber. The chamber is charged with liquid CO.sub.2, which turns to CO.sub.2 snow inside the chamber. As the CO.sub.2 sublimates, the vapors are free to travel below the false ceiling and into the cargo carrying compartment of the container, thereby cooling the cargo. In another mode of operation, the CO.sub.2 is charged into a bladder in the false ceiling and is vented to the ambient as pressure builds. This keeps the cargo cool without letting it come in contact with the CO.sub.2 vapor. Although this system has been found to be very effective in cooling various cargo, when utilized in conjunction with traditional shipping containers it is more difficult to maintain the low temperature because of the poor insulative qualities of the container.
Accordingly, it is an object of the present invention to provide an improved container for shipping refrigerated items.
Another object of the present invention is to provide an improved method for utilizing the cooling system disclosed in U.S. Pat. No. 4,761,969.
Yet another object of the present invention is to provide a refrigerated shipping container that is lighter than traditional containers yet is capable of carrying the same loads.
Still another object of the present invention is to provide a shipping container that may be cooled to the desired temperature by non-mechanical means and maintain that temperature without further charging or use of mechanical means for a longer period of time than traditional containers.
These and other object of the present invention are attained by the provision of an insulated shipping container. The floor, roof, endwall, doors and sidewalls are made from a light, non-metal, highly insulative material. These components generally comprise two relatively thin sheets of the insulative material separated by support channels. The cavities between the sheets are filled with foam insulation. Reinforcing rods may also be utilized to pre-load the structure before packing the cargo in the container. The walls, floor, doors, and roof are assembled on the support structure such that no surface of the support structure extends from inside the container to the outside.
These and other objects and useful features of the present invention will now become evident to those skilled in the art from the following detailed description of the preferred embodiments.